Electrical fuse for rotary current generator with rectifier

ABSTRACT

The invention relates to an electrical fuse for rotary current generators, having a rectifier assembly ( 14 ) for supplying a DC network, in particular in motor vehicles. To achieve simple, cost-effective and rapid-response fuse performance in the event of an overload, it is provided that a fuse element ( 21 ) be disposed in a line strand, carrying all the generator current, between the rectifier assembly ( 14 ) and a DC connection terminal ( 22 ) of the generator.

The invention relates to an electrical fuse for rotary currentgenerators, having a rectifier assembly for supplying a DC network, inparticular in motor vehicles, as generically defined by the preamble tothe main claim.

PRIOR ART

In motor vehicles, to an increasing extent electrical devices are beingused to improve the comfort and safety of the motor vehicles. Forsupplying these devices from the on-board electrical system of the motorvehicles, in by far the most cases, rotary current generators are used,which have a high power density and are thus under severe thermal loads.A rectifier assembly is as a rule integrated with the housing of therotary current generators, so that only the DC output of this assemblyforms the connection terminals of the generator, to which the connectioncables of an accumulator battery of the on-board vehicle electricalsystem are connected. In the event of an overload or a short circuit atthe generator or the rectifier assembly, which not infrequently happensin motor vehicles whenever a battery charging device is connected to thedischarging battery with the wrong polarity, not only can the generatoror the rectifier assembly be destroyed, but this can also trigger stillfurther damage to the vehicle.

To avoid these dangers, it is already known from German Patent DE 30 01522 C2, to dispose fuse elements in the rectifier assembly, between theconnections of the positive and negative diodes of the three rectifierbridges. The fuses, which because of production variations have onlyvery imprecise response values, are formed by line portions bent in aloop from recesses in a printed circuit board of the rectifier assembly;these loops melt open in the event of an electrical overload and can betemporarily repaired again by twisting the ends together. Since theterminals of the thus-protected power diodes of the rectifier assemblyare soldered or welded to the printed circuit board, once a fuse hasresponded, the entire rectifier assembly later has to be replaced, whichis expensive and time-consuming. Moreover, there is the risk that thefuse that has responded will be only temporarily repaired or in otherwords bypassed, without the rectifier assembly being replaced at thenext opportunity. In that case, the risk of destruction and overheatingincreases quite considerably. If the response of a fuse in one of thethree rectifier bridges goes unrecognized, the two intact rectifierbridges are then loaded all the more heavily, so that finally they failas well.

The object of the present invention is to accomplish protection of thegenerator and the rectifier assembly from electrical overload or shortcircuit as simply and reliably as possible.

ADVANTAGE OF THE INVENTION

The electrical fuse of the invention having the characteristic of thebody of claim 1 has the advantage over the prior art that when the fuseresponds, the generator along with the rectifier assembly is shut offcompletely, making the response of the fuse clearly apparent from theinterruption in the charging process. A further advantage is that if abattery charging device is connected with the wrong polarity, it is nolonger necessary—as it was until now—for all three fuses in the threerectifier bridges to respond; instead, from the response of one fuse,the generator is completely disconnected from the on-board electricalsystem, thus averting the risk of overheating.

Advantageous refinements and embodiments are attained from the othercharacteristics recited in the dependent claims. For instance, anespecially expedient embodiment that is simple from a productionstandpoint is obtained if the fuse element is disposed between a heatsink, forming the positive pole, of the bridge rectifier and a positiveconnection bolt of the generator. The positive connection bolt isfastened in insulated and detachable fashion in a hole of the positiveheat sink.

For the sake of changing the fuse as easily as possible if the fuse hasresponded, it is expedient to slip the fuse element, together with aninsulator part embracing the head of the positive connection bolt, ontothe positive connection bolt and to be put into electrical contact withit on the face end of the head. For the sake of the most reliablepossible contacting, it is also proposed that the positive connectionbolt, insulator part and fuse element form a prefabricated componentunit, in that the fuse element is galvanically connected, preferablywelded, by one terminal, to the connection bolt head, on the face endthereof. In this case, the complete component unit is replaced after thefuse has responded.

The most reliable and simple connection of the fuse element to thepositive heat sink is attained in that with its other terminal, the fuseelement is embodied annularly and is placed on a collar, embracing theconnection bolt, of the insulator part, and this terminal, on its topside, is put into electrical contact with the positive heat sink bypressure when the connection bolt is tightened.

Very simple production of the fuse element can be achieved in that thefuse element is a stamped metal part, which between its two terminalshas a portion of narrowed cross section, embraced laterally on the headof the positive connection bolt by the insulator part, which portionmelts away in the event of an overload.

To prevent a direct connection of the positive heat sink to the positiveconnection bolt and thus to prevent bypassing of the fuse element, aninsulating disk is advantageously placed on the positive connection boltabove the positive heat sink, in order to insulate the heat sink from aprotective cap secured in a manner known per se to the connection bolt.

As alternative to the aforementioned replacement of the entire componentunit with the fuse element, the embodiment can expediently also bedesigned in terms of its construction such that only the fuse elementhas to be replaced after its response. In that event, it is providedthat the positive connection bolt is embraced at its head region by aninsulator part and protrudes in insulated fashion through the hole inthe positive heat sink, the fuse element being placed on the positiveconnection bolt in such a way that with its lower terminal, it rests onthe positive heat sink, and with its upper terminal, it is put intoelectrical contact with the positive connection bolt by means of a nut.

Also in this respect, it is provided that the fuse element is embodiedof an annular, disklike insulating substrate body, which on each of itstwo face ends has a respective annular-disklike terminal, and a meltingportion of narrowed cross section is moved laterally past the insulatingsubstrate body between the two terminals.

For the sake of safety, to make it possible to fasten the portion thatmelts away upon response of the fuse in a predetermined position, secureagainst rotation and positionally securely, on the positive connectionbolt, this portion is guided around a platelike protrusion, formedlaterally onto the insulating substrate body, that embraces the meltingportion on both sides. In addition, this protrusion is positionallyfixed on both sides by lugs that are formed onto the positive heat sink.

Since this fuse element can also be put on the market as a spare part,the insulating substrate body must not fall out between the twoterminals of the fuse element before installation. To that end, it isprovided that the two annular-disklike terminals of the fuse elementembrace the insulating substrate body on its outer edge, in each case bymeans of angled tongues.

DRAWING

Further details of the invention are described in further detail in thetwo exemplary embodiments described below in conjunction with theassociated drawing.

Shown are:

FIG. 1, the circuit of the rotary current generator along with therectifier assembly and the fuse;

FIG. 2, as a first exemplary embodiment, the positive connection boltwith the fuse as a prefabricated component unit, and

FIG. 3, a sectional view of the positive connection bolt with the fuse,mounted on the positive heat sink;

FIG. 4, as the second exemplary embodiment, a cross section of therectifier assembly in the region of the positive connection bolt;

FIG. 5, in a three-dimensional view, the fuse element seated on thepositive connection bolt in a manner secure against relative rotation;and

FIG. 6, in fragmentary section, a variant of the second exemplaryembodiment of FIG. 4.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In FIG. 1, the three phases 10 of a rotary current generator are shown,which by one end are combined into a “Y” connection and by their otherend are connected to a respective diode bridge 11, 12 and 13 of arectifier assembly 14. For interconnection of the three phases 10 to thethree diode bridges, there is a printed circuit board 15, and each ofthe three diode bridges comprises one negative diode 16 and positivediode 17 connected in series. The negative diodes are press-fitted onthe anode side into a negative heat sink 18, and the anode terminals ofthe negative diodes 16 are thus combined by means of the negative heatsink 18 to form a negative terminal 19. The positive diodes 17 arepress-fitted on the cathode side into a positive heat sink 20. In thisheat sink 20, the cathode terminals of the positive diodes 17 arecombined and connected via a fuse element 21 to a positive terminal 22of the rectifier assembly 14. The fuse element 21 is dimensioned suchthat in order to protect the generator and the rectifier diodes 16, 17,it melts open if the allowable maximum direct current (DC) is exceeded,and thus interrupts the current circuit on the generator side. This canhappen for instance in the event of incorrect polarity when a batterycharging device is connected.

FIG. 2 shows a prefabricated component unit 24 comprising a positiveconnection bolt 25, an insulator part 26 shown in section, and the fuseelement 21. The positive connection bolt 25 forms a DC connectionterminal of the rotary current generator for the positive connectioncable of an accumulator in the on-board electrical system of a motorvehicle. The insulator part 26 is embodied such that it embraces thehead 27 of the connection bolt 25. It is also provided with a collar 26a that embraces the shaft 25 a. The fuse element 21 is slipped onto thepositive connection bolt 25 together with the insulator part 26 and putinto electrical contact with the head 27 on the face end 27 a of thehead, being solidly welded by its lower terminal 29 to the face end 27 aof the head 27. With its upper terminal 30, it is embodied annularly andis slipped onto the collar 26 a of the insulator part 26. The fuseelement 21 is a stamped metal part, which between its two terminals 29,30 has a portion 31 of narrowed cross section, embraced laterally on thehead 27 of the positive connection bolt 25 by the insulator part 26,which portion melts away in the event of an overload.

In FIG. 3, the positive connection bolt 25 is shown together with thefuse element 21 and a protective cap 32, in cross section mounted on thepositive heat sink 20. The shaft 25 a of the connection bolt 25protrudes in insulated fashion through a hole 33 in the positive heatsink 20, and the collar 26 a of the insulator part 26 protrudes into thehole 33, and furthermore the lower edge 33 a of the hole 33 rests on thetop side of the upper terminal 30 of the fuse element 21. The upper edge33 b of the hole 33 carries an insulating ring 34, on which theprotective cap 32, via a spring disk 35, is braced with an injectedclamping disk 36. The parts are tightened against one another by a nut37 placed on the positive connection bolt 25. On the one hand, thispressure-contacts the positive heat sink 20 to the upper terminal 30 ofthe fuse element 21, and on the other hand the positive heat sink isinsulated by the insulating ring 34 from the clamping disk 36 of theprotective cap 32 and thus also from the nut 37 and the connection bolt25, to prevent electrical bypassing of the fuse element 21.

Since the fuse is disposed, in the form of a fuse element 21, 40, in aline segment that carries all the generator current between therectifier assembly 14 and a generator connection terminal 22, 25 of thegenerator, in the event of a response upon an overload the fuse element21 can easily be replaced. Since the positive connection bolt 25 issecured detachably in the positive heat sink 22, in that event theentire component unit 24 of FIG. 2 can be replaced.

In a second exemplary embodiment shown in FIGS. 4 and 5, the sameelements have the same reference numerals as in the first exemplaryembodiment. However, here the fuse element 40 is embodied such thatafter response, it can be replaced by itself. Once again the positiveconnection bolt 25 is embraced here in its head region 27 by aninsulator part 41, which with a collar 41 a protrudes into the hole 33of the positive heat sink 20. The fuse element 40 is placed on the endof the positive connection bolt 25 that protrudes through the hole 30 insuch a way that it rests with its lower terminal 29 on the positive heatsink 20. With its upper terminal 30, it is put into electrical contactwith the positive connection bolt 25 by means of the nut 37, in thatfirst a contact disk 42 rests on the upper terminal 30. Onto thiscontact disk 42, the protective cap 32 is now placed, with the clampingdisk 36 injected on the edge of the fastening opening 38, onto thepositive connection bolt 25. The protective cap 32, contact disk 42,fuse element 40, heat sink 20 and insulator part 41 are finallytightened firmly with the nut 37 placed on the thread of the connectionbolt 25.

The fuse element 40 here comprises an annular, disklike insulatingsubstrate body 43, with one annular-disklike terminal 29, 30 on each ofits two end faces, and with a melting portion 31 a of narrowed crosssection, which is moved laterally past the insulating substrate body 43between the two terminals 29, 30 and which melts away in the event of anoverload. From the three-dimensional view in FIG. 5, it can be seen thatthe melting portion 31 a is guided around a platelike protrusion 43 a,formed laterally onto the insulating substrate body 43, that embracesthe melting portion 31 a on both sides. For positional fixation of thefuse element 40 on the positive connection bolt 25, two lugs 44 areformed onto the positive heat sink 20, which embrace the protrusion 43 aof the insulating substrate body 43 on both sides and thus embrace it ina manner secure against relative rotation. In addition, the parts of thefuse element 40 are held together in such a way that the twoannular-disklike terminals 29 and 30 each embrace the insulatingsubstrate body 43 by means of angled tongues 45.

The positional fixation of the fuse element 40 has the advantage that itcan thus be assured that melting portion 31 a will not come into contactwith metal components of the rectifier assembly and thus bypass the fusefunction. This also prevents the melting portion 31 a from coming intocontact with temperature-sensitive materials, such as the protective cap32, and finally, the positional fixation makes it possible to shift therectifier assembly with the fuse element 40 placed on it, without anychange occurring in its position. The spacing of the two lugs 44, whichcan be embodied in any arbitrary cross-sectional shape, on the positiveheat sink 20 from one another should be selected such that the fuseelement 40 can be inserted with its protrusion 43 a between the two lugs44 without restriction in the joining direction. This positionalfixation is possible without additional components, since it can berecessed out of an existing mold for the positive heat sink, usingsimple tools.

If the rectifier assembly and the protective cap 32 are embodied suchthat the melting portion 31 a of the fuse element 40 has an adequatesafety spacing from them anyway, then a positional fixation of the fuseelement can also be omitted. FIG. 6 shows an alternative version forthis purpose, in which the protrusion 43 a on the insulating substratebody 43 has been left out. Here, the fuse element 40 a is placedannularly onto the positive connection bolt 25 and tightly fastenedbetween the positive heat sink 20 and the contact disk 42 by the nut 37.Its melting portion 31 a can be seated at any arbitrary point on thecircumference of the insulating substrate body 43.

What is claimed is:
 1. An electrical fuse (21, 40) for rotary currentgenerators, having a rectifier assembly (14) for supplying a dc network,in particular in motor vehicles, characterized in that the fuse isdisposed, in the form of a fuse element (21, 40), in a line segmentcarrying all the generator current, between the rectifier assembly (14)and a generator connection terminal (22, 25) of the generator, whereinthe fuse element (21, 40) is disposed between a heat sink (20), formingthe positive pole, of the rectifier assembly (14) and a positiveconnection bolt (25) of the generator, forming the generator connectionterminal (22), and the positive connection bolt (25) is secured ininsulated fashion and detachably on the positive heat sink (20) in ahole (33) in the positive heat sink (20).
 2. The electrical fuse ofclaim 1, wherein the fuse element (21), together with an insulator part(26) that embraces the head (27) of the positive connection bolt (25),is slipped onto the positive connection bolt (25) and put intoelectrical contact with it on the face end (27 a) of the head (27). 3.The electrical fuse of claim 2, wherein the positive connection bolt(25), insulator part (26) and fuse element (21) form a prefabricatedcomponent unit (24), in that the fuse element (21) is galvanicallyconnected, preferably welded, by one terminal (29), to the connectionbold head (27), on the face end (27 a) thereof.
 4. The electrical fuseof claim 3, wherein with its other terminal (30), the fuse element (21)is embodied annularly and is placed on a collar (26 a), embracing theconnection bolt (25), of the insulator part (26), so that this terminal,on its top side, is put into electrical contact with the positive heatsink (20) by pressure.
 5. The electrical fuse of claim 4, wherein thefuse element (21) is a stamped metal part, which between its twoterminals (29, 30) has a portion (31) of narrowed cross section,embraced laterally on the head (27) of the positive connection bolt (25)by the insulator part (26), which portion melts away in the event of anoverload.
 6. The electrical fuse of claim 2, wherein an insulating ring(34) is placed on the connection bolt (25) on the positive heat sink(25), in order to insulated the positive heat sink (20) from aprotective cap (32) that is secured in a manner known per se on theconnection bolt (25).
 7. The electrical fuse of claim 1, wherein thepositive connection bolt (25) is embraced at its head region (27) by aninsulator part (41) and protrudes in insulated fashion through the hole(33) in the positive heat sink, the fuse element (40) being placed onthe positive connection bold (25) in such a way that with its lowerterminal (29), it rests on the positive heat sink (20), and with itsupper terminal (30), it is put into electrical contact with the positiveconnection bolt (25) by means of a nut (37).
 8. The electrical fuse ofclaim 7, wherein the fuse element (40) is embodied of an annular,diskilke insulating substrate body (43), which on each of its two endshas a respective annular-disklike terminal (29, 30), and a meltingportion (31, 31 a) of narrowed cross section is moved laterally past theinsulating substrate body (43) between the two terminals (29, 30). 9.The electrical fuse of claim 8, wherein the melting portion (31 a) isguided around a platelike protrusion (43 a), formed laterally onto theinsulating substrate body (43), that embraces the melting portion (31 a)on both sides.
 10. The electrical fuse of claim 9, wherein theprotrusion (43 a) of the insulating substrate body (43) is embraced andpositionally fixed on both sides by lugs (44) formed onto the positiveheat sink (20).
 11. The electrical fuse of claim 8, wherein the twoannular-diskilke terminals (29, 30) of the fuse element (40) embrace theinsulating substrate body (43) on its outer edge, in each case by meansof angled tongues (44).
 12. The electrical fuse of claim 7, wherein acontact disk (42) slipped onto the positive connection bolt (45) restson the upper terminal (29) of the fuse element (40) and is firmlyfastened, together with the fuse element (40) and the positive heat sink(20), on the positive connection bolt (25) by the nut (37).
 13. Theelectrical fuse of claim 12, wherein a clamping disk (36) injected intoa fastening opening (38) of a protective cap (32) is fastened betweenthe contact disk (42) and the nut (37).